3D printing is an additive manufacturing process for making three-dimensional objects of arbitrary shapes from digital models. In 3D printing, successive layers of a material are laid down adjacently to form the objects. Typically a round or ribbon like material is extruded through a movable nozzle.
U.S. Pat. No. 5,121,329 describes fusion deposition modeling, wherein an extruder is moved in a rectangular coordinate system while producing a stream or ribbons of melted thermoplastic material. The ribbons are laid down adjacent to each other to produce layers that fill the volume of the desired object.
U.S. Pat. No. 5,866,058 describes controlling a local environment to maintain the extruded material below a solidification temperature, and above a creep relaxation temperature while making objects.
Generally, objects produced by prior art methods have the undesirable property of severe anisotropic tensile strength variation. The individual ribbons of melted thermoplastic have an axial strength close to the bulk strength of the material, but inter-ribbon and inter-layer bonding strengths vary greatly.
For example as shown in FIG. 1 for injection-molded acrylonitrile butadiene styrene (ABS), the individual ribbon axial tensile strength is about 30 Mega Pascal (MPa), with a 45/−45 degree crisscross and a 0/90 orientation composite at around 20 MPa, and a traverse (ribbon to ribbon) strength of about 2 MPa, or about 1/15th of the ribbon's axial strength.
Special polymers, such as ABS functionalized with polymethylmethacrylate (PMMA) as described in U.S. 20090295032 can improve the bonding. High cost materials, such as polyetherimides, can produce parts with a minimum strength of 35 MPa in the inter-layer bond strength and with a maximum of 90 MPa as the individual ribbon tensile strength, which is a 2:1 strength discrepancy, but still far better than the 15:1 ratio of the conventional ABS.
U.S. Pat. No. 5,906,863 describes adding short fibers to a thermosetting mixture, such as a ceramic slurry, to produce a “green part” with oriented fibers. A specific method to control the orientation is not described.
Most prior art 3D printers are based on a three degree of freedom linearly orthogonal (XYZ) manipulation of the work piece and extruder.
Some 3D printers use rotating discs or a cylinder as a support base, see WO 2011/011818, in order to provide a more uniform surface for spreading of powder that will later be glued, solvent-bonded, or laser-sintered.